This invention relates to radar systems, and more particularly, to radar systems providing instantaneous ranging from parameters determinable entirely at a passive location.
Methods known in the past employed for passive location of radar emitter sources required the knowledge of several parameters related to the operation of the emitter source measurements made from two or more known spatial locations, and/or the known rate of relative motion of the emitter source.
In a first known method, knowledge of the waveform modulation of the emitter source in the time or frequency domain was required. An example of such a requirement included the scan rate, the pulse duration, the pulse interval and/or the frequency modulation patterns.
In a second known method, measurements had to be provided in the form of the emitter signal angle of arrival or the emitter signal time of arrival. Measurements in the form of the angle of arrival were described in the process of triangulation while measurements in the form of time of arrival where described in the process of trilateration. The emitter signal measurements of angle and time of arrival were then employed in conjunction with the time and location of the measurements to ascertain emitter location.
The third known method utilized for determining the range to a radar emitter involved the measurement of angular rates between the emitter source and the measurements site/platform.
Further, the prior art also included a method and an apparatus wherein a passive station can determine its position relative to a transmitting station which is stationary or moving. The transmitting station transmits a narrow pulsed scanning beam and the passive station can utilize the pulses received directly from the transmitting station and the reflected pulses received from a plurality of scatterer objects. The apparatus employs a direction finding antenna to determine a bearing of the transmitter station relative to the passive station. Further, a set of differential time signals are measured for transmitting a pulse from the transmitter to each of the scatterer objects and then to the passive station. Also, a set of transmitter pointing angles is determined, the pointing angles located between the transmitter-scatterer lines and the transmitter-passive station line. A second set of angles is determined to locate each scatterer-passive station line with respect to the transmitter-passive station reference line. A set of ranges is calculated from the above data and then averaged and weighted for the position determination.
Each of the previously described methods are very involved requiring data of a plurality of parameters. Thus, a major problem exists when the compilation of data is not available. It is highly desirable that the range to the emitter source be established when the waveform of the emitter signal is unmodulated or is randomly modulated. It is further desirable that the range to emitter source be established by requiring only those measurements available from a single location and that the knowledge of relative motion between the emitter source and the measurement platform is not necessary.
Hence, those concerned with the development and use of passive measurement systems in the radar field have long recognized the need for improved passive ranging systems which enable the determination of the emitter range when the waveform of the emitter signal is unmodulated or randomly modulated, when parameter measurements are available only from a single location and when knowledge of the relative motion between the emitter source and the measurement platform is not available. The present invention fulfills all of these needs.